DETERMINANTS OF METABOLIC COST OF SUBMAXIMAL CYCLING

Abstract

DETERMINANTS OF METABOLIC COST OF SUBMAXIMAL CYCLING J McDaniel and J. C. Martin, University of South Carolina [email protected] (Sponsor A. R. Coggan, FACSM) Previous investigators have reported that the metabolic cost (MC) of producing mechanical power (MP) varies with pedaling rate (PR) during submaximal cycling. PR, however, constrains two physiological phenomena. PR constrains the rate at which muscles are activated and relaxed. PR, in combination with crank length (CL), determines pedal speed (PS) which constrains muscle shortening velocity. The purpose of this investigation was to determine the physiological mechanism(s) primarily responsible for differences in MC associated with producing MP at different PR. A secondary purpose was to determine if CL per se directly affects MC. Trained male cyclists (N = 9, age: 33 ± 7 years, mass 80 ± 13 kg, VO2 max: 66 ± 7 ml/kg/min) cycled at 30, 60, and 90% of their individual lactate threshold on three crank lengths (145, 170, and 195mm) and at four pedaling rates (40, 60, 80, and 100rpm). MC was determined by indirect calorimetry and MP was recorded with an SRM dynamometer. The linear and quadratic effects of MP, PR, and PS on MC were evaluated using stepwise multiple regression analysis. The stepwise procedure indicated that MC was significantly related to MP, PS, and PS2 (R2 = 0.98). These results suggest that the main physiological determinant of the cost of producing mechanical power is muscle shortening velocity. Further, they suggest that neither CL nor PR directly affect MC. Rather, the importance of those two variables is manifested in their effects on PS or muscle shortening velocity.